In recent years, biometric authentication technology has been developed for authenticating a user of an apparatus or system based on a biometric image representing biometric information such as the pattern of veins of the hand or finger, a fingerprint, palm print, etc. A biometric authentication device which utilizes such biometric authentication technology, for example, acquires a biometric image representing the biometric information of the user who is trying to use the biometric authentication device as the input biometric image. Further, the biometric authentication device compares the input biometric information of the user which is represented in the input biometric image with the registered biometric information which is a biometric information represented in biometric images of registered users registered in advance. If it is determined as a result of comparison that the input biometric information matches the registered biometric information, the biometric authentication device authenticates the user as a registered user having a legitimate right. Further, the biometric authentication device allows the user which was authenticated use of a system in which the biometric authentication device is built or another system which is connected to the biometric authentication device.
Such biometric authentication technology desirably has the characteristic structure of the biometric information clearly captured in the biometric image in order to compare a user with a high precision. However, depending on the positioning of the part of the body including the biometric information utilized for the comparison with respect to the sensor for inputting the biometric information, in the biometric image, part of the biometric information which should be used for the comparison will not be captured or the biometric information will end up becoming unclear.
For example, when the biometric authentication device acquires an image capturing the vein pattern of the hand of a user as a biometric image representing biometric information, if the hand as a whole is not included in the range of capture of the sensor, the obtained image will end up only capturing part of the vein pattern of the hand. Alternatively, if the hand strays far from the ideal position of the hand with respect to the sensor, the image of the vein pattern of the hand which is represented in the obtained image will be small and as a result detailed parts of the vein pattern will end up becoming unclear on the image.
In this way, if part of the biometric information which is represented in the biometric image is missing or if the biometric information is unclear, the biometric authentication device can no longer use the information of the missing part or unclear part for the comparison. For this reason, the biometric authentication device can no longer accurately examine the degree of match of the vein pattern represented in the image registered in advance and the vein pattern represented in the input image for that missing part or unclear part. As a result, the precision of comparison ends up falling.
Therefore, technology is being developed for reinputting the biometric image for a user when judging if a biometric image is suitable or not and judging that it is not suitable (see Japanese Laid-Open Patent Publication No. 8-161491 and Japanese Laid-Open Patent Publication No. 2003-337949).